# Threshold Dynamics of a Semiconductor Single Atom Maser

## TL;DR

This paper reports on a semiconductor double quantum dot-based single-atom maser, demonstrating threshold behavior and transition from incoherent to coherent emission, aligning with existing maser theory.

## Contribution

It introduces a dynamic tuning protocol for controlling the DQD's repumping rate and studies the transition through the masing threshold in a semiconductor system.

## Key findings

- Demonstrated threshold behavior consistent with single atom maser theory
- Developed a protocol to controllably increase the repumping rate
- Measured the crossover from incoherent to coherent photon emission

## Abstract

We demonstrate a single-atom maser consisting of a semiconductor double quantum dot (DQD) that is embedded in a high quality factor microwave cavity. A finite bias drives the DQD out of equilibrium, resulting in sequential single electron tunneling and masing. We develop a dynamic tuning protocol that allows us to controllably increase the time-averaged repumping rate of the DQD at a fixed level detuning, and quantitatively study the transition through the masing threshold. We further examine the crossover from incoherent to coherent emission by measuring the photon statistics across the masing transition. The observed threshold behavior is in agreement with an existing single atom maser theory when small corrections from lead emission are taken into account.